Osten and friends.... almost one year ago, I too was facing a burned band
switch in my FL2100Z amp and it was not a pretty sight! With help, I finally
got the amp back on the air. In my particular case, I had bought the amp
used and believed (based on the sellers comments) that it was working fine.
That was my mistake -- but that's another story.
I believe the band switch let go or burned because of a parasitic in the
amp -- especially apparent on 15m. The oscillation was so bad, you could
tune up on 15m and turn in and out of the point of parasitic oscillation --
you should have heard it sizzle. Eventually -- and much to my surprise, the
band switch gave in to its parasitic pain with a huge flash of white light,
a corresponding big bang and the tell-tale smell of burnt electronic
components. The damage done by the failed band switch was extensive! It
included both tubes and a variety of other parts. This repair was to prove
very expensive before all was said and done. I contacted YAESU in California
to order the $100 USD switch and was told the it had been discontinued. I
subsequently found all the replacement wafer parts in a friends huge junk
box. The new tubes were sourced from
http://www.vacuumtubes.net/page/indexc.html in Florida for about $40 USD
each; they are Chinese tubes.
The original band switch adds additional capacitance progressively as you
switch to 80 and 160m. It is 100pF on 80 and 350pF on 160m. Given I couldn't
duplicate that process on junk box wafer replacement, we hard-wired the
correct capacitance directly for 80 and 160 respectively. Prior to
disassembly, everything was tagged and labeled. With the original switch out
and dissembled, the replacement (junk box) wafers were easy to add. With the
band switch back in all wiring was reattached as per the labeling. For
brevity in this story, I'll leave out the embarrassing part about my own
stupidity in the overall process -- but suffice to say I learned a great
deal about amplifiers through the overall repair process. Given this was my
very first amp, I went into this repair knowing almost nothing and come out
of the experience with a healthy respect for doing things right the first
time.
The one single addition made to the amp in the repair -- that ironically
cost the least -- that I think is a must for this amp is a
Parasitic-Suppressor Retrofit-Kit for the pair of 572B's. While there are a
variety of opinions on the subject of parasitics, in my case it really
works! My source was: http://www.vcnet.com/measures/.
For a graphic explanation of the event, I've put together a series of images
regarding the repair at: http://www.bcdxc.org/yaesu_fl2100z.htm.
73 de Paul, VE7AVV
StoneyGround Station
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